Question

等差数列{an}中,已知ak+a(k+1)+a(k+2)+a(k+3)+a(k+4)=A,则

Answer 1

ak+a(k+1)+a(k+2)+a(k+3)+a(k+4)=A

[ak+a(k+4)]+[a(k+1)+a(k+3)]+a(k+2)=A

2a(k+2)+2a(k+2)+a(k+2)=A

5a(k+2)=A

a(k+2)=A/5